The present invention relates to electronical scanning type medical ultrasonic imaging systems and more particularly to ultrasonic probes used in such measuring systems.
Current typical medical ultrasonic imaging systems obtain a sectional image of a human body using a ultrasonotomograph in B-mode display on a real-time basis. In the actual diagnosis, the diagnostician continuously alters the direction of a probe to obtain an image of a body region of interest to thereby presume the internal structure and tissue of the body. However, according to this method, it is difficult to intuitively know the position of the internal sectional area of the body as well as to obtain the sectional image of the same region with high reproducibility. In order to obtain the sectional image of a body region of interest, the diagnostician may press the body of the patient for a long time to thereby give an uncomfortable feeling to him or her. A diagnostic device is being demanded which is capable of continuously obtaining a plurality of sectional images of different regions of a human body to thereby permit easy presumption of a three-dimensional structure and tissue of the body.
In such device, it is necessary to control the directivity of ultrasonic waves in a two-dimensional direction in the transmission/reception. To this end, the use of an ultrasonic probe which comprises transducer elements in a two-dimensional array and separate signal lines connected to the corresponding elements is required. However, according to this system, as the number of transducer elements increases, the connection of signal lines becomes difficult, so that it is very difficult to manufacture, in a mass production basis, probes where the characteristics of the respective elements are constant.
U.S. Pat. Nos. 4,448,075 and 4,736,631 disclose an array type ultrasonic probe which is capable of altering its transverse aperture against electronical scanning direction. Such probe is composed of driving electrodes spatially arranged in parallel on one surface of a transducer plate and grounding electrodes spatially arranged in parallel on the other surface of the plate. The electrodes are disposed spatially intersecting so as to be orthogonal to each other. By the selection of a driving electrode, an ultrasonic beam is scanned and, by the selection of a grounding electrode, the width of a transducer aperture perpendicular to the scanning direction is changed. Thus, a single B-mode sectional image is obtained to thereby improve the directivity of the ultrasonic beam normal to the cross section over a wide depth range Especially, in U.S. Pat. No. 4,736,631, the probe utilizes an electrostrictive material which piezoelectricity is induced by a bias voltage. A bias voltage is applied to a selected matrix position to thereby prevent the occurrence of electroacoustic conversion at a non-selected matrix position by an electric field distribution through the non-selected electrodes. Thus, the control of the directivity of the acoustic beam perpendicular to the scanning direction is effected more accurately.